This invention relates to devices for the treatment of heart disease and particularly to endo-arterial prosthesis, which are commonly called stents. More particularly, the invention relates to catheter assemblies for removably securing the stent to the catheter during delivery through a body lumen.
Several interventional treatment modalities are presently used for heart disease including balloon and laser angioplasty, atherectomy and by-pass surgery. In typical balloon angioplasty procedures, a guiding catheter having a preformed distal tip is percutaneously introduced through the femoral artery into the cardiovascular system of a patient in a conventional Seldinger technique and advanced within the cardiovascular system until the distal tip of the guiding catheter is seated in the ostium. A guide wire is positioned within an inner lumen of a dilatation catheter and then both are advanced through the guiding catheter to the distal end thereof. The guide wire is first advanced out of the distal end of the guiding catheter into the patient""s coronary vasculature until the distal end of the guide wire crosses a lesion to be dilated, then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient""s coronary anatomy over the previously introduced guide wire until the balloon of the dilatation catheter is properly positioned across the lesion. Once in position across the lesion, the balloon, which is made of relatively inelastic materials, is inflated to a predetermined size with radiopaque liquid at relatively high pressure (e.g., greater than 4 atmospheres) to compress the arteriosclerotic plaque of the lesion against the inside of the artery wall and to otherwise expand the inner lumen of the artery. The balloon is then deflated so that blood flow can be resumed through the dilated artery and the dilatation catheter can be removed therefrom. Further details of dilatation catheters, guide wires, and devices associated therewith for angioplasty procedures can be found in U.S. Pat. No. 4,323,071 (Simpson-Robert); U.S. Pat. No. 4,439,185 (Lindquist); U.S. Pat. No. 4,516,972 (Samson); U.S. Pat. No. 4,538,622 (Samson, et al.); U.S. Pat. No. 4,554,929 (Samson, et al.); U.S. Pat. No. 4,616,652 (Simpson); U.S. Pat. No. 4,638,805 (Powell); U.S. Pat. No. 4,748,982 (Horzewski, et al.); U.S. Pat. No. 5,507,768 (Lau, et al.); U.S. Pat. No. 5,451,233 (Yock); and U.S. Pat. No. 5,458,651 (Klemm, et al.), which are hereby incorporated herein in their entirety by reference thereto.
One problem which can occur during balloon angioplasty procedures is the formation of intimal flaps which can collapse and occlude the artery when the balloon is deflated at the end of the angioplasty procedure. Another problem characteristic of balloon angioplasty procedures is the large number of patients which are subject to restenosis in the treated artery. In the case of restenosis, the treated artery may again be subjected to balloon angioplasty or to other treatments such as by-pass surgery, if additional balloon angioplasty procedures are not warranted. However, in the event of a partial or total occlusion of a coronary artery by the collapse of a dissected arterial lining after the balloon is deflated, the patient may require immediate medical attention, particularly in the coronary arteries.
A focus of recent development work in the treatment of heart disease has been directed to endoprosthetic devices called stents. Stents are generally cylindrically shaped intravascular devices which are placed within an artery to hold it open. The device can be used to prevent restenosis and to maintain the patency of a blood vessel immediately after intravascular treatments. In some circumstances, they can also be used as the primary treatment device where they are expanded to dilate a stenosis and then left in place.
One method and system developed for delivering stents to desired locations within the patient""s body lumen involves crimping a stent about an expandable member, such as a balloon on the distal end of a catheter, advancing the catheter through the patient""s vascular system until the stent is in the desired location within a blood vessel, and then inflating the expandable member on the catheter to expand the stent within the blood vessel. The expandable member is then deflated and the catheter withdrawn, leaving the expanded stent within the blood vessel, holding open the passageway thereof.
However, retaining the position of the stent in the proper location on the expandable member while advancing the catheter through the body lumen has been found to be difficult. If the stent is dislodged from or moved on the expandable member the system will not correctly deliver the stent into the body lumen. This would require repeating the procedure. This delays insertion of the stent into the body lumen and lengthens the time of the stenting procedure.
Different methods have been attempted to maintain the position of the stent on the expandable member. One such method involves a protective sheath surrounding the catheter and stent assembly, which is retracted prior to inflation of the expandable member. The use of the sheath, however, increases the profile of the catheter assembly which must traverse narrow vessels and the sheath reduces the flexibility of the distal end of the delivery catheter. It would be an improvement to use a technique which does not increase the overall profile of the catheter assembly and maintains the flexibility of the delivery catheter.
Another method has been to remove the friction reducing coating on the expandable member in the location of the stent thereby allowing the catheter assembly""s pre-coated surface to hold the stent in frictional contact. This method has not proven highly efficient in maintaining the stent in the desired location.
What has been needed and heretofore unavailable is a highly efficient means of maintaining a stent in a desired location on a stent delivery system without increasing the overall profile of the catheter assembly or compromising the flexibility. The present invention satisfies this need.
This invention is directed to an improvement in stent delivery systems for removably securing a stent onto an expandable member. Securing the stent is accomplished by tightly crimping the stent onto the balloon portion of a catheter wherein a deformable foamed material has been disposed. By compressing the deformable foamed material the stent is secured due to the increased frictional contact and interference between the stent and the compressed catheter assembly.
Stent delivery systems are typically composed of an elongated tubular member, or catheter, encompassed by an expandable member such as an inflatable balloon. The stent is located about the expandable member so that the two can be expanded together. The improvement of this invention includes introducing a compressible foamed cover into the space between the tube member and the expandable member. The foamed cover may be adhered to the elongated tube member, the expandable member, or injected into the space therebetween. The stent is then crimped onto the expandable member so that the foamed cover is compressed. The foamed cover may be compressed with sufficient force to form pockets of material within the foamed cover corresponding to gaps within the structure of the stent. The foamed cover may also extend beyond one or both of the longitudinal ends of the stent so that sufficient crimping force can be applied on the expandable stent to form ridges in the foamed cover located beyond the ends of the stent.
This invention can be used with the known configurations of stent delivery catheter assemblies including over-the-wire (OTW) intravascular catheters and rapid exchange (Rx) intravascular catheters.
The foamed cover may be composed of any soft polymer, such as polyurethane elastomers, polyamide block copolymers, polyester block copolymers and polyolefins. It is contemplated that the foamed cover is softer and more flexible than when in its solid form. The foam density, cell openness and cell size can be optimized to provide desired stent security and desired profiles.
The present invention results in a simplified method of inserting the stent into the body lumen. The catheter assembly is inserted into the body lumen without further steps being taken to secure the stent. The expandable member is inflated at the desired location expanding and implanting the stent within the body lumen. When the expandable member is then deflated, the stent is released and the remainder of the catheter assembly may be withdrawn leaving the stent implanted within the body lumen.
Other features and advantages of the invention will be come apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the features of the invention.